Semiconductor device

ABSTRACT

A semiconductor device, wherein a first metallic member is bonded to a first electrode of a semiconductor element via a first metallic body containing a first precious metal, and a second metallic member is bonded to a second electrode via a second metallic body containing a second precious metal.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device, particularly,to a semiconductor package having a structure which is adequate fordecreasing the electrical resistance of the semiconductor packagewithout a Si chip.

An example of a conventional transistor package is disclosed inJP-A-8-64634 (1994). A semiconductor chip, whereon electronic circuitsare formed, is bonded to a die pad for heat release at a rear planeelectrode side by welding. A bump is formed on an Al electrode at acircuit formed plane side of the chip, and an inner lead is connectedelectrically and mechanically thereon. An inner lead is also connectedto the die pad, and the chip, the die pad, and a part of the lead issealed with resin so as to cover them. In a case when the bump issolder, the lead side is plated with tin (Sn), gold (Au), or solder, andthe like, and bonded with the bump by melting the solder of the bump. Ina case when the bump is gold, the lead is plated with tin, and bondedwith the bump by an Au—Sn eutectic reaction. The inner lead is composedof three lines provided for a source electrode, a drain electrode, and agate electrode, respectively. The lead for the source electrode ismanufactured in a comb teeth shape. A through opening to the resin isformed on the head.JP-A-5-121615 (1993) discloses a surface mountingtype semiconductor package having a wireless structure as anotherconventional example. Three external connection terminals are connectedto electrode terminals of the semiconductor chip. Two electrodes on anupper surface of the chip are connected to the external connectionterminals by thermocompression bonding of Au balls. Mounting on acircuit substrate is performed by soldering the tip region of the leadterminals, which protrude forward and backward from the chip mountingportion, to the terminals of the substrate.

In accordance with a conventional standard surface mounting typesemiconductor package, the semiconductor chip is bonded to the die padof the lead for the drain by soldering, and the source electrode and thegate electrode of the semiconductor chip are connected to the leads forthe source and the gate of the external connection terminals by Al wirebonding. The chip, each respective lead, and a part of the die pad aremolded with resin. The die pad is exposed at the bottom of the resinbody so as to allow the structure of the resin body to be connected tothe circuit substrate, and its size is set to be larger than the size ofthe resin mold.

In accordance with the conventional chip die pad bonding structure of asemiconductor chip, a bonding structure using a resin with conductiveparticles, wherein Pb rich solder having a low yield strength or Agparticles are mixed, has been adopted in order to prevent the chip fromgenerating a high stress when the chip is fixed to a member made of a Cubase alloy.

The electrical resistance of the semiconductor package without a Si chipin the surface mounting type plastic package of a conventional verticalsemiconductor element has been from several tens mΩ to ten and severalmΩ with a wire bonding structure. In accordance with advancement ofsemiconductor technology, the on-resistance of the element has beendecreasing year by year, and at present, a device of several tens toseveral mΩ/cm² has been developed. Further decrease of the resistancecan be expected in future. In that case, a decrease of the electricalresistance of the semiconductor package without a Si chip isindispensable for improving the performance of the semiconductorpackage, because the electrical resistance of a semiconductor packagewithout a Si chip becomes larger than the device resistance. A priortechnique regarding the on-resistance of the semiconductor package isdisclosed in JP-A-8-64634. The prior proposed technique relates to aninsert mounting type package. The insert mounting type package is notrestricted in size, and a thick and large size die pad can be used,because the bonding between the substrate and the lead is strongstructurally. Therefore, a decrease of the electrical resistance of thesemiconductor package without a Si chip is relatively easy. However, thesurface mounting type package has a property that the fatigue strengthof the bonding portion is weaker than that of the insert mounting typepackage, because it has a structure in which the tip of the leadsprotruding from both sides of the resin body are bonded to the terminalof the substrate by soldering two planes of small area to each other.Therefore, it is necessary to absorb the thermal strain between thepackage and the substrate resulting from heat generation of the chipwhich causes deformation of the flexible leads. Accordingly, it isnecessary to make the shape of the leads thin and slender. In this case,a decrease of the electrical resistance of the semiconductor packagewithout a Si chip is difficult, because the electrical resistance of thelead itself is large.

In the case of a surface mounting type package, the above problem can besolved by adopting a structure wherein the die pad mounting the chip issoldered directly to the circuit substrate. However, if a position wherethe lead, to be connected to the electrode at an upper surface of thechip, protrudes from the resin body differs in height from the positionwhere the die pad protrudes, the contacting planes of the upper andlower metal molds for molding the resin form a three dimensionalstructure, such that a problem is created in that the manufacture of themetal molds becomes difficult. The above problem becomes significantwhen the lead frame is a matrix frame (arranged in X and Y directions)and the objective is to manufacture a large number of the packages,simultaneously. The problem can be solved by making the size of the diepad to be contained in the resin body small, but if so, a pressingportion to press the die pad onto the bottom surface of the metal moldmust be provided in the metal mold, in order to expose the die pad atthe lower plane of the resin body. If the size of the die pad issufficiently large, it is possible to press the die pad onto the bottomsurface of the metal mold. However, if the size of the die pad is thesame as the size of the chip, the pressing portion can not be found onthe die pad, and a problem is created in that the die pad is moldedwhile being exposed at the bottom of the resin body. Therefore, in caseof a small size semiconductor package, wherein the size of the die padis the same as the size of the chip, it is difficult to assembly thestructure in such a manner that the die pad concurrently operating asthe external connection terminals of the rear electrode is contained inthe resin body.

On the other hand, conventionally, a soldering connection or an adheringstructure with a resin using conductive particles has been adopted forthe connection of the rear plane of the chip with the externalconnection terminals, such as a die pad, and others. The solderingconnection is a superior connection with regard electrical resistance,thermal resistance, and heat resistance reliability. However, currently,in view of environmental problems, no use of Pb is employed, and theconventional soldering material containing Pb must be replaced with anew bonding material containing no Pb. There are various solderingmaterials containing no Pb having a solidus line temperature below 250°C., but actually, there is no adequate soldering material containing noPb having a solidus line temperature higher than 270° C., which isdurable against severe mounting on the substrate of the package. Theonly exception is Au—Si solder having a solidus line temperature of 370°C. However, Au—Si solder can not be adopted as the soldering materialfor the electrode at the rear plane of the chip, for two reasons, suchas high cost and generation of cracks in the chip during the coolingstep after soldering when the size of the chip is large, because of thehigh yield strength. Therefore, a problem exists in that there is nosoldering material containing no Pb to replace the soldering materialcontaining Pb. On the other hand, adhesion with a resin with conductiveparticles is durable thermally in a short time against the necessarytemperature for the mounting ,.i.e. 270° C., but is weak in mechanicalstrength, because the adhesion strength is maintained by the resin. Eventhough tightness of the adhesion is reinforced with a shrinking force bycuring the molding resin, a package having a large area or a packageused in a high temperature has a problem in that the electric resistanceand thermal resistance at the bonding portion are increased inaccordance with deterioration of the resin, which is caused by a changewith elapsing time or temperature cycles. In particular, because the oneplane molding structure, wherein the die pad (external connectionterminals) is exposed to the surface of the resin body, is a structurewhich can not receive sufficient pressing force from the molding resinat the rear plane of the chip, a problem is raised in that the long termreliability of the resin using conductive particles for adhesion isfurther decreased.

SUMMARY OF THE INVENTION

The present invention has been achieved in consideration of the aboveproblems, and has the object of providing a semiconductor devicecomprising a package structure which can decrease the electricalresistance of the semiconductor package without a Si chip.

The semiconductor device in accordance with the present invention isprovided with a semiconductor element, which comprises a semiconductorsubstrate, a first electrode provided at the front plane of thesemiconductor substrate, and a second electrode provided at the rearplane of the semiconductor substrate. A first metallic member isconnected to the first electrode of the semiconductor element via afirst metallic body containing a first precious metal, and a secondmetallic member is connected to the second electrode of thesemiconductor element via a second metallic body containing a secondprecious metal.

In accordance with the present invention, the electrical resistance ofthe semiconductor package without a Si chip can be decreased, becausethe first and second members are connected to the electrodes of thesemiconductor element via the metallic bodies containing differentprecious metals.

In accordance with the above composition, the surface portion of thefirst metallic member and the surface portion of the second metallicmember for connecting to the external wiring are desirably positioned inapproximately the same plane. The term “approximately the same plane”means, for instance, a plane of the wiring substrate or circuitsubstrate of various electronic devices, whereon electronic members aremounted. Accordingly, the semiconductor device can be mounted onto thewiring substrate or the circuit substrate.

As the first metallic body, there is an protrusion electrode whichprotrudes from the first electrode or the first metallic member of thesemiconductor device. As the protrusion electrode, there are bumpelectrodes, or ball electrodes made of precious metal, such as gold (Au)or silver (Ag), and others can be used. In order to decrease theelectrical resistance of semiconductor package without a Si chip, aplurality of the protrusion electrodes are desirably arranged withapproximately the same interval relative to each other on the wholesurface of the bonding interface of the first electrode with the firstmetallic member.

As the second metallic body, a metal layer positioned at the bondinginterface of the second electrode with the second metallic member can beused. The metal layer is desirably composed by bonding the respectiveprecious metal layers positioned at bonding front plane sides of thesecond electrode and the second metallic member, respectively. As thematerial of the precious metal layer, a precious metal selected from agroup consisting of gold (Au), silver (Aq), platinum (Pt), palladium(Pd), and the like, or an alloy containing the above element as a maincomponent can be used. A layer composed of plural kinds of preciousmetals, or multi-layers of the alloy layer is also usable. Furthermore,any bump electrode or ball electrode made of precious metal, such asgold (Au) or silver (Aq), silver (Ag) particles mixed with resin, asilver (Ag) member in a shape of plate, sheet, or network, and a silvermember shaped in plate or sheet having bumps and dips, or cavityportions thereon, may be interposed between the precious metal layerpositioned at the second electrode side and the precious metal layerpositioned at the second metallic member side. As the desirable othermetal layer, an alloy layer containing precious metal as a maincomponent, of which the solidus line temperature is higher than 400° C.,is usable. As the material of the alloy layer, an alloy of silver (Ag)and tin (Sn) containing silver as the main component can be used.

A precious metal layer may be provided on the bonding surface of thefirst and second electrodes, and of the first and second metallicmembers of the semiconductor device. As the material of the aboveprecious metal layer, a precious metal selected from a group consistingof gold (Au), silver (Ag), platinum (Pt), palladium (Pd), and the like,or an alloy containing the above element as a main component can beused. As the material of the first and second electrodes of thesemiconductor device, aluminum, or an aluminum alloy such asaluminum-silicon can be used.

The first and second metallic members electrically connect the first andsecond electrodes of the semiconductor element to external electrodes,the wiring substrate, the circuit substrate, and others. For instance,the first and second metallic members are lead wire, lead electrodes, ordie pad terminals, which are a part of the semiconductor package, andothers, or a part of these members. In order to decrease the electricalresistance of a semiconductor package without a Si chip, the firstmetallic member desirably comprises plural portions extending from theportion having the bonding portion with the first electrode, and theplural portions each comprise a surface portion for connecting withexternal wiring. In accordance with the circuit substrate or wiringsubstrate connecting to the semiconductor device, each surface portionas described above of the first metallic member is provided with aconductor portion (for instance, copper foil) for electrical connection.The conductor portions are connected electrically on the circuitsubstrate or the wiring substrate. For instance, a continuous conductor(for instance, copper) pattern can be used as the conductor portion ofthe printed substrate.

The composition of the semiconductor device in accordance with thepresent invention as described above can be applied to semiconductordevices, wherein the semiconductor element and the first and secondmetallic members are coated with an insulating material, such as theresin sealing type or resin molding type semiconductor devices. In thesecases, the rear plane of the bonded plane of the first metallic memberbonded with the first electrode has desirably an exposed portion forconnecting with external wiring. In addition to the above composition,the bonded plane side of the semiconductor element is used as a circuitforming plane (for instance, a plane whereon one of the main currentelectrodes and a control electrode of the vertical semiconductorswitching element are formed), and the first electrode is desirably usedas the main current electrode. In accordance with the semiconductordevice, wherein the semiconductor element and the first and secondmetallic members are coated with an insulating material, the rear planeof the bonded plane of the second metallic member bonded with the secondelectrode may have an exposed portion for connecting with externalwiring. As the insulating material, ceramics and other insulators can beused, in addition to various resins.

The various composition described above can be used concurrently.However, some compositions have a function and an advantage to decreasethe electrical resistance of the semiconductor package without a Si chipby itself, such as the other semiconductor device of the presentinvention described hereinafter.

As the other semiconductor device of the present invention, thesemiconductor package, which contains a semiconductor element comprisinga first electrode and a second electrode on the front plane and the rearplane of the semiconductor substrate, respectively, can be composed inany one of the following ways:

1) A composition, wherein the second electrode and the second metallicmember are bonded via a metallic layer; the metallic layer is composedby bonding precious metal layers, one of which is provided on thebonding front plane of the second electrode, and another one of which isprovided on the bonding front plane of the second metallic member.

2) A composition, wherein the second electrode and the second metallicmember are bonded via an alloy layer; the alloy layer is composed of analloy containing precious metal as a main component, of which thesolidus line temperature is higher than 400° C.

3) A composition, wherein the first metallic member comprises pluralportions extending from the bonding portion with the first electrode,and each of the plural portions comprises a surface portion forconnecting with external wiring.

The composition of 1) or 2), and the composition 3) can be usedconcurrently.

Each of the semiconductor devices of the present invention describedabove can be applied to various semiconductor elements, such as a MOS(Metal Oxide Semiconductor) field effect transistor, a MIS (MetalInsulator Semiconductor) field effect transistor, a bipolar transistor,an insulated gate bipolar transistor, a diode, or integrated circuits,and the like. The composition of each of the semiconductor devices ofthe present invention is preferably applied to the semiconductorelement, wherein the first electrode and the second electrode are usedas a pair of main current electrodes; and to the vertical typesemiconductor element, such as a power MOSFET and power transistor,wherein the first and the second electrodes are used as the main currentelectrodes, and the main current passes vertically in the semiconductorsubstrate in a direction from the first electrode at the front planeside to the second electrode at the rear plane side, or in a reversedirection. In this case, the on-resistance or on-voltage between theterminals including the package can be decreased, accompanied with lowon-resistance characteristics of the semiconductor element.

In accordance with the semiconductor device of the present invention,the bonding strength of the Au bump/Al electrode bonding portion isimproved by changing the Al film between the Au bump/Si substrate to anAu—Al compound in all the thickness direction of more than 80% of thebonding area by heating treatment of the Au bump/Al electrode bondingportion at a high temperature. Furthermore, the temperature cycle lifeis improved by forming a structure, wherein a compression load is addedto the bonding portion by filling a resin between the electrode lead andthe chip.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a top plan view, FIG. 1(b) is a cross-sectional view, andFIG. 1(c) is a bottom plan view of an embodiment of the semiconductorpackage of the present invention;

FIG. 2 is a cross-sectional view of another embodiment of thesemiconductor package of the present invention;

FIG. 3 is a cross-sectional view of another embodiment of thesemiconductor package of the present invention;

FIG. 4(a) is a cross-sectional view and FIG. 4(b) is a bottom plan viewof another embodiment of the semiconductor package of the presentinvention;

FIG. 5 is a diagram of an example of the lead frame used for thesemiconductor device of the present invention;

FIG. 6 is a diagram showing the assembled structure and assemblingmethod of the semiconductor package of the present invention;

FIG. 7 is a diagram of the lead frame structure during assembling of thesemiconductor package of the present invention;

FIG. 8 is a diagram illustrating the resin molding method for thesemiconductor package of the present invention;

FIG. 9 is a flow diagram of the assembling of the semiconductor packageof the present invention;

FIGS. 10(a), 10(b) and 10(c) are cross-sectional views showing anembodiment of the assembled structure of the semiconductor packagecontaining no Pb according to the present invention;

FIG. 11(a) is a top plan view and FIG. 11(b) is a cross-sectional viewsof an embodiment of the semiconductor package containing no Pb accordingto the present invention;

FIG. 12(a) is a cross-sectional view and FIG. 12(b) is a top plan viewof an embodiment of the bonding member containing no Pb for theelectrode at the rear plane of the chip according to the presentinvention;

FIG. 13 is a cross-sectional view of another embodiment of the bondingmember containing no Pb for the electrode at the rear plane of the chipaccording to the present invention;

FIG. 14(a) is a cross-sectional view and FIG. 14(b) is a top plan viewof another embodiment of the bonding member containing no Pb for theelectrode at the rear plane of the chip for the present invention;

FIG. 15 is a cross-sectional of another embodiment of the semiconductorpackage of the present invention;

FIG. 16 is a cross-sectional view of another embodiment of thesemiconductor package of the present invention;

FIG. 17 is a cross-sectional view of another embodiment of thesemiconductor package of the present invention;

FIG. 18 is a top plan view of an embodiment of the wiring substratemounting the semiconductor package of the present is invention;

FIG. 19 is a top plan view of an embodiment of the electronic devicemounting the semiconductor package of the present invention;

FIG. 20 is a diagram showing a current path model of the semiconductorpackage;

FIG. 21(a) is a cross-sectional view and FIG. 21(b) is a bottom planview showing a fundamental structure of the semiconductor package of thepresent invention;

FIG. 22(a) is a cross-sectional view and FIG. 22(b) is a top plan viewof an embodiment of the transistor package of the present invention;

FIG. 23 is a cross-sectional view of another embodiment of thetransistor package of the present invention;

FIG. 24 is a cross-sectional view of another embodiment of thetransistor package of the present invention;

FIG. 25 is a cross-sectional view of another embodiment of thetransistor package of the present invention;

FIG. 26 is a cross-sectional view of an embodiment of a cross sectionalstructure of the die pad-bonding film of the present invention;

FIG. 27 is a cross-sectional view of another embodiment of a diepad-bonding film of the present invention;

FIGS. 28(a), 28(b) and 28(c) are cross-sectional views representingsteps of a bonding method using the die pad-bonding film of the presentinvention;

FIG. 29(a) is a cross-sectional view of a bonded structure and FIG.29(b) is a graph indicating experimental data on the relationshipbetween the strength of an Au/Al bonding portion versus the holding timeat a high temperature for the bonded structure;

FIG. 30(a) is a cross-sectional view of a bonded structure according tothis invention, FIG. 30(b) is a cross-sectional view of a bondedstructure of the prior art, and FIG. 30(c) is a graph indicating anexperimental data on the relationship between the strength of Au/Albonding portion versus the holding time at a high temperature;

FIG. 31 is a cross-sectional view of an embodiment in which the bump ofthe front plane side electrode is alloyed with a metal having a lowmelting point;

FIG. 32 is a cross-sectional view of an embodiment in which thesemiconductor package shown in FIG. 31 is mounted onto the wiringsubstrate;

FIG. 33 is a cross-sectional view of an embodiment in which thesemiconductor package of the present invention is mounted while omittingthe die pad onto the wiring substrate;

FIG. 34 is a cross-sectional view of an embodiment in which a planemounting type semiconductor package of the present invention is mountedonto the wiring substrate; and

FIG. 35(a) is a top plan view and FIG. 35(b) is a cross-sectional viewof a semiconductor element used in the assembling of the semiconductorpackage of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first embodiment of the present invention is a structure assembledby the steps of: directly connecting a gate electrode and a sourceelectrode of a transistor chip to a metallic member for externalconnection (lead) via plural Au bumps arranged in an optimum manner;electrically and thermally connecting a drain electrode at the rearplane of the chip to the metallic member for external connection (diepad) to enclose the source electrode and any one of the metallic memberfor the gate electrode (lead) or the metallic member for the drainelectrode (die pad) inside of a polyhedral package. In accordance withthe above structure, the planes of the metallic member contained in thepackage can be bonded by soldering to a terminal plane of a wiringsubstrate. Desirably, the structure is assembled so as to extend tips ofthe leads or the die pad from the two side planes of the package, and tomake it possible to press the metallic member contained in the packageonto the bottom plane of the metal molds via the metallic member whichprotrudes from the package.

The second embodiment of the present invention is a structure, whereinthe drain electrode is bonded to the precious metal plated metallicmember (die pad) via any one of precious metal bumps, a mesh sheet madeof precious metal, precious metal particles, a thick precious metalplating having a hardness less than 60 Hv directly, or via an alloylayer having a solidus line temperature of at least 400° C., whichcontains a precious metal as a main component. The bonding portion canbe obtained by compression bonding using heating and ultrasonicvibration. Desirably, when the chip size is large, the structure isassembled by forming the Au bumps onto the source electrode and the gateelectrode on the circuit forming plane of the chip, and bonding theelectrodes directly to the lead plated with precious metal. Furthermore,the structure is assembled so that the size of the lead at the sourceelectrode side is made equal to the size of the die pad at the rearplane of the chip, and the members are arranged symmetrically, in orderto prevent the chip from being subjected to an increased bending stress.

The third embodiment of the present invention is a structure and amethod for assembling the structure by the steps of: forming a largenumber of Au bumps onto a source electrode and a gate electrode made ofAl on the chip; mounting the chip so as to be aligned with respectiveleads plated with precious metal; mounting a precious metal memberhaving a smaller hardness than the Au bump thereon; mounting a die padplated with precious metal thereon; and bonding all the contactingboundary planes simultaneously with heating, loading, and ultrasonicvibration by arranging a bonding tool, which applies pressure andultrasonic vibration, on the die pad.

The first embodiment will be explained in detail hereinafter.

A current path model of the semiconductor package is shown in FIG. 20.Respective reference marks are used to identify the following members.

184: external connection terminal for drain,

186: bonding portion,

182: electrode at the rear plane of the chip,

180: chip,

181: Al electrode,

185: metallic bump, and

183: external connection terminal for source (lead).

The electric resistance R between the external connection terminals forthe source and the external connection terminals for the drain isexpressed by the following equation (1):

R=R 1 +R 2 +R 3 +R 4 +R 5 +R 6 +R 7  (1)

The part obtained by eliminating the internal resistance R4 of the chip180 from the equation (1) can be regarded as the electrical resistanceof the semiconductor package without a Si chip. The resistance R6 of thebump 185 can be expressed by the following equation (2):

R 6=(ρ×h/S)/n  (2)

where,

ρ: specific resistance of the bump

h: height of the bump

S: cross sectional area

n: number of the bumps

The regular size of the Au bump is 150 μm in diameter and 20 μm inthickness, if the Au bump is formed by a ball bonding method with wire,which makes it possible to form the bump directly on the Al pad with alow cost. The resistance of the bump in the above case becomes (0.026/n)mΩ of sufficiently small size. The resistance R5 of the Al electrodefilm 181 can be expressed by the following equation (3):

R 5(ρ/4πt) 1 n(r 2/r 1)  (3)

where,

ρ: specific resistance of the electrode film

t: thickness of the electrode film

r2: the outer diameter of the electrode

r1: the diameter of the bump

The outer diameter of the electrode is approximately proportional to1/(n^(1/2)) when n bumps are arranged uniformly. Therefore, if n isincreased, the ratio r2/r1 comes to close 1, and the resistant R5 can bedecreased sufficiently by increasing the thickness of the electrode filmand the number of bumps. The resistance of the external connectionterminals (R1+R7) can be expressed simply by the following equation (4):

(R 1+R′ )=(ρ×L/S)  (4)

where,

ρ: specific resistance of the lead

L: current-carrying length of the lead

S: current-carrying cross sectional area

The resistance of the external connection terminals becomesapproximately 1.4 mΩ in the case of a regular SOP package for surfacemounting (thickness: 0.16 mm, width: 0.3 mm, length: 2 mm×2). That is,at a level where the electrical resistance of semiconductor packagewithout a Si chip is less than 1 mΩ, the electrical resistance ofsemiconductor package without a Si chip can not be decreased only byadopting the bump structure, and a structure to decrease the resistanceof the external connection terminals must be adopted.

Thus, in accordance with the semiconductor device of the presentinvention, a structure is used, which ensures the reliability of theconnecting portion of the external connection terminals with the wiringsubstrate in addition to providing a decrease in the resistance of theexternal connection terminals.

The fundamental structure of the semiconductor device 1 of the presentinvention is indicated in FIGS. 21(a) and 21(b). The only way todecrease the resistance of the external connection terminals is toincrease the cross sectional area of the current path or to decrease thelength of the current path. Therefore, one of the external connectionterminals has a structure in which the current path is increased in thethickness direction of the terminal. In this case, the current-carryingcross sectional area is sufficiently large, such as from several toseveral tens mm² in comparison with the current carrying distance(0.1-0.2 mm), with the result that the resistance of the first externalconnection terminal portion 194 can be made less than 1 μΩ. The secondexternal terminal portion 193 has a structure in which connection ismade with the terminal of the wiring substrate by descending along theside plane of the chip, whereby the current-carrying distance becomesseveral millimeters. However, two times the current-carrying crosssectional area can be ensured by using both sides of the package. Inaccordance with the present structure, a wide and thick member can beused as the second external connection terminal for a reason to bedescribed later. Therefore, more than several times the current-carryingcross sectional area can be ensured, and the electric resistance can bedecreased to approximately one-tenth in comparison with a conventionalpackage structure.

The conventional package structure has a problem in that, if therigidity of the second connection terminal is increased, the long termreliability at the connection portion with the wiring substrate isdecreased. However, in accordance with the structure of the presentinvention, the temperature cycle reliability can be ensured even if therigidity of the second connection terminal is high. The reasons for thisare that the temperature difference from the substrate is small becausethe structure is composed so that the area of the first externalconnection terminal at the bottom of the resin body is sufficientlylarge, and the chip, i.e. a heat source, and wiring substrate arelocated close each other, and that the thermal distortion is smallbecause the connecting terminal is made of a copper alloy having athermal expansion coefficient close to that of the substrate.Accordingly, the absolute value of the thermal distortion generated atthe connecting portion of the first and second connection terminals withthe substrate is small. A pressing force is generated at the connectingportion of the second connection terminal and the substrate withincreasing temperature because of the difference in thermal expansion ina height direction of the resin body from the Cu member corresponding tothe folded legs, and based on this effect, the temperature cyclereliability is improved in comparison with a conventional package, andthe rigidity of the second connection terminal can be increased.

During the molding step for assembling the package indicated in FIG.21(a), the first connection terminal member 194 can be pressed towardthe bottom plane of the metal molds via the precious metal bump 195 bypushing down the second connection terminal with the side wall of theupper die. Accordingly, the package, wherein the connection terminalsare certainly exposed at the bottom plane of the resin body, can beassembled without adding any special measures to the die. In this case,a particularly important point is that the second connection terminalmember connected via the bump protrudes from both side planes of theresin body. By pushing down at both sides of the second terminal member,generation of an inclination of the first terminal member and splittingoff of the bump can be prevented, and faultless resin molding having ahigh production yield becomes available. In accordance with a structureto push down at one side, a moment is generated between the diecontacting portion of the pushed down second terminal member and thelower die contacting portion of the first terminal member. Then, thebonding portion is split off by generation of a tensile stress at a partof the bump bonding portion, and a failure caused by resin flowing intothe bonding plane is generated by separating one side of the firstterminal member. Therefore, faultless resin molding with a highproduction yield can not be ensured.

Now, a second embodiment will be explained in detail. Thecharacteristics required for bonding at the rear plane of the chipinvolve four points, as follows:

1) electrically conductive and thermally high-conductive to the externalconnection terminal (die pad),

2) long temperature cycle life,

3) durability against a soldering temperature at the time of mountingthe package onto the substrate, and

4) possibility to bond a wide area of the rear plane of the chip duringa short time in a mass-production line with no undesirable influence.

Because no appropriate high melting point soldering material containingno Pb is available, the bonding satisfying the above characteristicsmust be achieved using materials other than a soldering material. When aprecious metal material is used as the bonding material, the thermalconductivity of the bonding material is approximately ten times that ofthe soldering material. Accordingly, even if the bonding has the samethickness, the same heat transfer characteristics can be obtained usingone tenth of bonding area if the bonding portions distribute heatuniformly at the rear plane of the chip. That is, it is significantlyadvantageous in heat releasing characteristics.

Regarding the temperature cycle life, it is significantly influenced bywhat component can absorb thermal strain caused by a difference ofthermal expansion of the chip and the external connection terminal (diepad) by deformation. In the use of conventional solder, most of thestrain could be absorbed by deformation of the solder, because the yieldstrength of the solder is very low, and the destruction occurs at thesoldering portion. In this case, the strain was scarcely transmitted tothe chip, and there was an advantage in that the stability andreliability of the chip was maintained. On the contrary when a preciousmetal material is used for the bonding, the yield strength is higherthan solder, and lower than Si and Cu. Accordingly, the strain on thechip and the die pad is increased, but the life of the bonding portionis extended. The amount of the strain added to the chip can be adjustedby providing cavities in the precious metal layer so long as the heatreleasing characteristics do not haves serious problem. One of thepractical measures is to provide cavities using a mesh sheet, particles,or a sheet having bumps and dents as the bonding material.

Regarding heat resistance, there is no problem. The most important pointis readiness of bonding and assembling. When precious metals were bondedto each other using a conventional thermocompression bonding method, itwas necessary to set the heating temperature in the range of 400-500°C., in order to bond in a short time. In accordance with this method,the amount of thermal strain during the cooling step was large, becausethe temperature difference from room temperature was significant,creating a large danger of destruction of the chip even in a case whenthe size of the chip is not remarkably large. In accordance with thepresent invention, a method has been adopted in which the bondingtemperature is specified as being equal to or below 250° C. in order tosolve the above problem, and ultrasonic vibration is utilized forachieving ensured bonding at the above temperature. However, when thechip is bonded to the die pad by a thermosonic bonding method, a problemis generated in that the chip is damaged at the portion where thecircuit forming plane of the chip contacts the hard bonding jig, becausethe ultrasonic vibration is added to the compression of the die pad andthe chip by holding them with a hard heating stage and a hard bondingjig. In accordance with the present invention, the above problem issolved by forming an Au bump onto the electrode at the circuit formingside of the chip; arranging an external connection terminal member(lead) having the same size with the die pad at the circuit formingside; and forming a structure, wherein the chip does not directlycontact the hard bonding jig, in order to prevent the chip from beingdamaged. When the bonding portions are provided at both upper and lowerplanes of the chip, respectively, generation of a variation in thebonding condition (a condition that one side is bonded tightly andanother side is not bonded well) is a concern. However, in accordancewith the ultrasonic vibration bonding method, if the bonding portionsare arranged in series to the bonding jig, a self adjusting function isachieved such that relative vibration at one portion is restricted inaccordance with the bonding at the portion, and the relative vibrationat the other portion, which is not bonded yet, is increased.Accordingly, two bonding portions having approximately the same strengthcan be obtained. However, when it is desired to enlarge the bonding areaat the rear plane of the chip in view of the heat release, it ispossible to provide different bonding areas by making the bondingmaterials at the upper plane and the rear plane of the chip differentfrom each other, whereby the bonding at the circuit forming plane sideof the chip is performed with a bonding material having a higher yieldstrength, and the bonding at the rear plane side of the chip isperformed with a bonding material having a lower yield strength. Byadopting the above bonding structure and bonding method, the bonding atthe rear plane of the chip with a high performance and high reliabilitybecomes possible without using Pb.

The operation and the advantages of the third embodiment are the same asdescribed in the second embodiment. The practical bonding time isapproximately several hundreds milliseconds except the time necessaryfor transferring and positioning the work, and is shorter than the timenecessary for conventional plural wire bonding operation. It isnecessary to form the Au bumps on the Al electrode of the chip,previously, but it does not influence to the production tact, and inview of a point that the chip-die pad connection and the bonding can beperformed simultaneously, the production tact can be decreased incomparison with the conventional operation.

EMBODIMENTS

Hereinafter, practical structures of the above embodiments of thepresent invention will be explained in detail with reference to thedrawings.

FIG. 1(a) is a top plan view, FIG. 1 (b) is a cross sectional view, andFIG. 1(c) is a bottom plan view of an embodiment of the semiconductorpackage of the present invention. In accordance with the drawings, thesemiconductor chip 1 is a vertical MOS transistor of 4×2 mm in size. Thefilm thickness of the Al electrodes 2, 3 for the source and gate isapproximately 4 μm, and Au is vapor deposited onto the surface of therear plane electrode 4, which is to be the drain electrode. A largenumber of Au bumps 8 are formed onto the source electrode and the gateelectrode of the chip by a ball bonding method, that is, in a mannersuch that the bumps are arranged with an approximately equal intervalover all of the surface of the electrodes. Each of the lead terminals 5,6, for the source and the gate has a structure, wherein the Cu core 11is plated with a precious metal 12 of Pd/Au, and its thickness is 0.2mm. The width of the lead terminal for the source 5 is approximately thesame as the source electrode 2. That is, the lead terminal for thesource 5 covers almost all the surface of the source electrode 2. The Aubump on the chip and the Pd/Au plane of each lead terminal is bondeddirectly by a thermosonic thermocompression bonding method with heatingat 230° C. The size of the Au bump bonded by the compression bondingmethod is approximately 120 μm in diameter and 40 μm in thickness. Theexternal connection die pad terminal 7 has a structure, wherein the Cucore 13 is plated with precious metal 14 of Pd/Au, and its one plane isfurther plated with Ag 15 to approximately 10 μm. The Au plane of therear plane electrode of the chip and the Ag plated plane of the die padterminal are bonded directly by a thermosonic thermocompression bondingmethod with heating at 230□ C., the same as the case of the Au bump/leadterminal. The lead terminal for the source protrudes outside from bothleft and right side walls of the molded resin body 16, and ismanufactured to be folded. The lead terminal having a wide width whichprotrudes leftward and rightward, is provided with the slit 10 and someopenings 9 at locations above the chip. The lead terminal for the gatealso protrudes outside from both left and right side walls of the moldedresin body 16. The die pad terminal for the drain is exposed at thebottom of the resin body. The lower plane of the die pad terminal (acontacting plane with the connection terminal on the wiring substrate),and the lower planes (the same contacting plane) of the lead terminalsfor the source and gate, which are manufactured to be folded, aremanufactured to be the same height, that is, to be the same plane.

In accordance with the present embodiment, the electrical resistance ofsemiconductor package without the Si chip can be decreased significantlyon account of its structure, wherein the source electrode and the leadterminals for the source are connected by a large number of Au bumpsarranged uniformly; the lead terminals having a wide width protrudesfrom both the left side and the right side; the die pad terminals areconnected directly to the rear plane electrode by the Ag plated film;the cross sectional area of the current path to the wiring substrate islarge; and the conducting distance is very short (equal to onlythickness of the substrate). Accordingly, a novel semiconductor deviceprovided with an unprecedented semiconductor package having a lowelectrical resistance without the Si chip, such as lower than 1 mΩ , canbe obtained. Additionally, an advantage in that the semiconductorpackage is superior in long term reliability is realized, because thepresence of the Au bumps of 40 μm in thickness on the circuit plane andthe Ag plated film of 10 μm in thickness on the rear plane of the chipat the connecting portion of the chip to the Cu terminal operates as acushion material, because Au and Ag are soft materials (yield strengthis low) in comparison with the Cu terminal material, and an effect toprevent the chip from being influenced by a large force is realized; andAu and Ag have a longer temperature cycle life than that of solder. Whenthe semiconductor package is mounted onto the wiring substrate, thepackage is bonded with the substrate via a wide area of the die padterminal, and the chip, i.e. a heater, and the substrate are connectedby the shortest distance under a preferable thermal conductingcondition. Accordingly, the thermal strain generated between thesubstrate and the package is small, because the temperature differencebetween the package and the substrate is small, and the thermalexpansion coefficient of the substrate and the thermal expansioncoefficient of the Cu terminal are close to each other. Therefore, anadvantage is realized in that the connecting portion of thesemiconductor package with the wiring substrate has a long temperaturecycle life and a superior long term reliability. Furthermore, becausethe openings are provided at the lead terminal for the source positionedabove the chip, generation of voids in the resin molding step can beprevented by two effects, such as supplying the resin through theopenings and degassing through the openings can be performed even if theAu bumps are flattened and the gap between the lead terminal and thechip is decreased. Accordingly, the reliability of the package can bemaintained.

A semiconductor package having a connecting structure of high heatresistance and high temperature cycle reliability can be provided,because thermosonic bonding Au/Ag is performed via a Ag plated filmserving as the connecting structure of the rear plane electrode of thechip with the die pad terminal, which results in solderless bonding.

Here, the size of the Au bump is 120 μm in diameter. However, a largersize bump such as several hundreds μm in diameter is desirable, ifformation of the bump is possible. By increasing the size of the bump,the resistance can be further decreased, the bonding strength isincreased, and an advantage is realized in that the production yield isincreased, because peeling off the bump bonding portion by an externalforce during assembly of the package can be prevented effectively.

FIG. 2 indicates an embodiment of the semiconductor package of thepresent invention, wherein the Ag bump compression bonding method isapplied to the chip-die pad connection. In accordance with FIG. 2, theAl electrode 22 of the semiconductor chip 21 and the lead terminal 26plated with precious metal 25 are bonded tightly to each other via theAu bumps 30. The rear plane electrode 23 of the chip and the die padterminal 29 plated with precious metal are bonded to each other via theAg bumps 31. The reference numeral 27 in FIG. 2 indicates a Cu core, andthe reference number 28 indicates a precious metal. The one side of thelead terminal is cut off at a portion near the side wall of the resinbody 32, and the other side of the lead terminal is manufactured to befolded and aligned at the same height as the die pad in order to connectwith the terminals of the wiring substrate.

In accordance with the present embodiment, deformation can be absorbedstructurally, because the chip and the die pad are connected by the Agbumps. Therefore, the temperature cycle life at the bonding portion ofthe die pad terminal/chip is significantly long, and a semiconductorpackage containing no Pb, which is desirable in view of environmentalproblems, and having a high reliability can be provided. The mountingreliability is improved significantly, because thermal strain is hardlyadded to the solder bonding portions of the connecting terminals of thewiring substrate. The size of the package can be decreased to anequivalent size as the chip, the thickness of the package can bedecreased to approximately 1 mm, and a small size semiconductor packagefor surface mounting, which is appropriate for high density mounting,can be provided.

FIG. 3 indicates an embodiment of the semiconductor package of thepresent invention, wherein the Ag paste adhering method is applied tothe chip-die pad connection. In accordance with FIG. 3, the Al electrode36 of the semiconductor chip 35 and the lead terminal 40 plated withprecious metal 39 are bonded tightly to each other via the Au bumps 45.The reference numeral 38 in FIG. 3 indicates a Cu core, and thereference numeral 44 indicates a peripheral plane of the die padterminal. The rear plane electrode 37 of the chip and the die padterminal 43 are adhered to each other by the Ag paste 46. The die padterminal has a structure wherein the Cu core 41 is plated with Pd/Au 42,and its peripheral planes are manufactured by counter boring in order toproduce an anchor effect relative to the molding resin. The leadterminals protrude out from both sides of the resin body 47.

In accordance with the present embodiment, the same advantages as theembodiment indicated In FIG. 1 can be obtained. Because the peripheralplanes of the die pad terminal are manufactured to have a shape whichenables the die pad to be engaged with the resin, the die pad terminalcan be pressed to the rear plane of the chip by the shrinking force ofthe molding resin. Therefore, even if the chip/die pad connecting methodusing Ag paste, which makes for easy assembling, is adopted, a reliablesemiconductor package can be provided.

FIGS. 4(a) and 4(b) are directed to an embodiment of the semiconductorpackage of the present invention, wherein the package structure enablesthe mounting of the circuit forming plane toward the wiring substrate.As shown in the drawing, plural Au bumps 57 are formed on the Alelectrodes 51, 52 for main current and for control on the circuitforming plane of the semiconductor chip 50, respectively, as in theembodiment indicated in FIG. 1; and the external connection terminal formain current 55 and the external connection terminal for control 56,which have a size equivalent to the size of each electrode and arecontainable in the resin body 59, are bonded thereon by a thermosonicthermocompression bonding method. The surface of each externalconnection terminal is plated by Pd/Au flush plating. The rear planeelectrode 53, the outermost surface of which is composed of a Au or Agvapor deposition film, is formed at the rear plane of the chip, and theexternal connection terminal 54 for rear electrode, Cu surface of whichis plated by Pd/Au flush plating, is bonded thereon by thermosonicthermocompression bonding method interposing an Ag mesh sheet 58 platedwith Sn of 0.1-5 μm in thickness between them. The external connectionterminals for main current and for control are molded in a condition inwhich they are exposed to the surface of the resin body, and theexternal connection terminals for the rear plane electrode protrude outfrom both left and right sides of the resin body. The one side of theexternal connection terminals for the rear plane electrode is cut off,and the other side is manufactured to be folded.

In accordance with the present embodiment, the same advantages as theembodiment indicated in FIG. 1 are achieved. Furthermore, cooling of thepackage can be performed most effectively and the temperature rise atthe Al electrode portion can be suppressed to a small amount, becauseits structure enables the circuit forming plane of the chip, i.e. aheater of the chip, to release heat effectively to the wiring substrate.As a result, the product life under conditions of practical use can beimproved significantly, because the thermal strain generated between theexternal connection terminals and the chip can be made small, andgrowing compounds between the Al electrode film and the Au balls can besuppressed.

FIG. 5 indicates an embodiment of a matrix lead frame for the source andgate electrodes used for assembling the semiconductor package of thepresent invention; FIG. 6 illustrates the bonding method duringassembling of the package as seen from the cross section A-A′ in FIG. 5;FIG. 7 shows the appearance of the matrix lead frame after bonding; andFIG. 8 is an illustration representing the resin molding method. Inaccordance with FIG. 5, a unit, wherein the lead for source 61 and thelead for gate 62 make up a pair to form the unit, is arranged in a X-Ydirection. The reference numeral 63 in FIG. 5 indicates an inner leadframe, and the reference numeral 64 indicates an outer lead frame. Inaccordance with FIG. 6, the Au bumps 71 formed previously on the Alelectrodes 66, 67 of the semiconductor chip are positioned and mountedonto the leads for the source 61 and for the gate 62 of the matrix leadframe. The reference numeral 75 in FIG. 6 indicates a heater. The diepad terminals 69 for the drain, whereon the Ag bumps 70 are formedpreviously, are mounted onto the chip rear plane electrode 68. Thebonding portions at the upper surface and the lower surface of the chipare bonded simultaneously by heating the heating stage 74 for mountingthe matrix lead frame at 200° C., and compressing the die pad terminalsusing the bonding tool 73, which produces ultrasonic vibration 76, witha force of 50-500 g per bump. In accordance with the ultrasonicvibration, the bonding operation is performed while controlling theflattened amount of the bumps, and the preciseness of the height of thelead and the die pad is controlled to be within a designated range. Thedirection of the ultrasonic vibration is restricted to the longitudinaldirection (up and down direction in FIG. 5), where the rigidity of thelead is high, in order to prevent the bonding portion from generatingbonding failure by resonance of the lead. The die pad terminal ismanufactured by punching it out from a large Cu plate which is platedpreviously with precious metal, because the die pad terminal isseparated and assembled individually. The state wherein the matrix leadframe (FIG. 7) after completion of the bonding is set in a metal mold isindicated in FIG. 8. FIG. 8 indicates a cross sectional structure asseen from the direction perpendicular to the A-A′ cross section in FIG.7. In accordance with FIG. 8, the cavities 82 of the metal molds 80, 81are formed to match the arrangement of the matrix lead frame and arearranged in the X-Y direction. Escaping spaces 83 for containing leadhangers are provided. The matrix lead frame is set into the cavity ofthe lower die 81 by positioning the semiconductor chip 65 so as to becontained therein, and then, the upper die is placed thereon andcompressed. The height of the source and gate leads extending out fromthe cavity is adjusted to be equal to or somewhat higher than the depthof the cavity in the lower die, and its structure is composed so that,when the leads are held by the side walls of the upper and lowercavities, the die pad terminal is compressed toward the bottom of thecavity. The leads are pressed down at left and right sides as the chipportion is in the center. However, if the amount of the pressing down istoo large, the leads may be subjected to the bending deformation, and atensile stress is generated at the Au bump portion of the middle of thechip. Therefore, in order to make the bending deformation of the leadsin a convex shape at the middle of the chip as small as possible, thelead holding portion of the upper die is manufactured in the shape ofknife, and the lower die is made to have a step, inner side of which islower than the outer side, so as to deform the leads in a W-shape.Regarding the molding resin, the size of the silica particles forlowering the thermal expansion is decreased so as to improve theefficiency of filling of the resin into the gap of 10-20 μm between thebump bonding portion, in order to prevent generation of resin voidsduring the pressure-injecting process.

In accordance with the lead frame and its manufacturing method, low costsemiconductor packages can be provided with the following effects. TheIC units are arranged in a matrix state in the lead frame for assembly,and the productivity can be increased by increasing the number ofpackages taken from a lead frame; the die can be manufactured withoutincreasing its cost, because the matching planes of the dies, except forthe lead holding portions, can be manufactured precisely by surfacegrinding manufacturing; decreasing the number of manufacturing steps ispossible, because the die pad-chip connection and the circuit formingplane side connection can be performed simultaneously by one bondingstep. Additionally, as a structural feature, a small and thinsemiconductor package close to the size of the chip can be provided.

FIG. 9 indicates an embodiment relating to the steps for assembling thesemiconductor package of the present invention. In accordance with FIG.9, four components are used in assembling the semiconductor package. Thesemiconductor chip is provided with Au bumps, which are formed at waferlevel, and cut pieces by dicing. Formation of the Au bumps can beperformed by any one of various known methods, such as a ball bondingmethod, a plating method, and an Au ball transcription method. Thereference character (4) in FIG. 9 indicates a Ag sheet. The externalconnection terminals for the source and gate are manufactured andreshaped by a punching method or an etching method from a Cu alloy platein a matrix lead frame shape, and after plating Ni onto the surface ofthe terminal as a base, Pd is plated to approximately 0.02-1 μm thereon.Finally, the terminals are finished by plating its outermost surfacewith Au to approximately 0.001-1 μm thick. The external connectionterminals for the drain is manufactured by plating the surface of a Cutape with Ni as a base, Pd is plated to approximately 0.02-1 μm thickthereon, the outermost surface of the terminals is plated with Au toapproximately 0.001-1 μm thick, and finally, the Cu tape is cut intopieces of plates having an equivalent size to the chip, The Ag sheet forthe chip-die pad connection is manufactured by forming the bumps anddips on one side or both sides of a Ag tape of 10-100 μm thick bypressing, and plating Sn of approximately 0.1-5 μm thick thereon. Thethickness of the Sn at this time is determined so that the weight ratioof Sn to Ag becomes equal to or less than 20% by weight. Finally, the Agsheet is cut to pieces of plates having an equivalent size to theexternal connection terminal for the drain or the chip. Each of thecomponents are bonded simultaneously per one IC as a unit, aftermounting the matrix lead frame onto the bonding stage, laminating in theorder of the semiconductor chip, the Ag sheet, and the externalconnection terminals after positioning each relative to the other, andheating, pressing, and ultrasonic vibrating simultaneously. Afterfinishing the bonding of all the matrix, the resin molding step isperformed by the same procedure as the embodiment indicated in FIG. 8.Finally, the semiconductor packages connected in a matrix state are cutand separated into pieces, and the semiconductor package is completed bymanufacturing the lead to fold and reshape.

In accordance with the present embodiment, manufacturing steps for thecomponents can be performed in parallel lines, and an incorporatedproduction of a large number of packages is possible; and in theassembling line only three steps are employed, including (1) setting thecomponents and bonding, (2) resin molding, and (3) cutting and reshapingthe lead, with the result that one step can be omitted in comparisonwith the conventional chip-die pad connection and wiring bondingprocess. Furthermore, the total production time can be decreased, andsignificant improvement in the productivity can be realized, because theabove step (1) assembly can be performed with less time than the timefor wire bonding.

FIGS. 10(a) to 10(c) are directed to indicates an embodiment of abonding structure of the chip rear plane electrode of the presentinvention. The lead frame is assembled with two lead frames, such as thelead frame for the source and gate, and the lead frame for the drain.The reference numerals 94 and 96 in FIG. 10 indicate an outer leadframe, respectively. As seen in the drawing, the lead frame made of Cualloy forming the lead for source 91 and the lead for gate 92, and thelead frame forming the die pad for drain 95 are plated with Pd/Au allover the surface thereof. The Au ball bumps 101 are formed on the diepad for the drain by the ball bonding method. In accordance with thisstructure, the semiconductor chip 97 having a rear plane electrode 102,wherein the Au ball bumps 100 are formed previously on the Al electrode98, is interposed between the above two kinds of lead frames, and theupper portion and the lower portion of the chip can be bondedsimultaneously. FIGS. 11(a) and 11(b) are directed to an example of thesemiconductor structure, which is obtained by molding the above bondedbody with resin, and reshaping the lead. As seen in the drawing, thesource lead 91 and the gate lead 92 protrude out from one side wall ofthe resin body 103, the lead for drain protrude out from the otheropposite side wall, and each of the leads is manufactured by a foldingprocess. The neck portion 93, which comprises a locally slender portion,is provided to the leads in the resin body, in order to provide astructure, wherein the stress generated at the folding process is hardlytransmitted to the bonding portion of the bumps. The height of theprotruded position of the leads at the left side differs from that atthe right side. Accordingly, the matching planes of the upper metal moldand the lower metal mold are manufactured with a single step. The rearplane of the chip has a compression bonded structure consisting of Audeposition film/Ag bumps 101/Pd/Au plated die pad, and the upper surfaceof the chip has a compressed structure consisting of Al electrodes 98,99/Au bumps 100/Pd/Au plated leads 91, 92. The reference numeral 104 inFIG. 11 indicates lead for a drain.

In accordance with the present embodiment, a semiconductor packagecontaining no Pb, which is desirable in view of environmental problemcan be provided. Additionally, the heat resistance of the package ishigh because the chip-die pad structure is composed by direct bonding ofprecious metals via the Ag bumps; and temperature cycle reliability ofthe package is high because THE thermal strain between the chip/die padcan be relaxed by the Ag bumps. The lead has a desirable wettabilitywith solder. As A result, the assembling process of the package can beshortened and productivity is increased, because the solder platingafter assembling the package becomes unnecessary. Additionally, anadvantage is realized in that a small and thin semiconductor is packagecan be provided, because the chip can be molded with resin with a sizeclose to the chip size.

FIGS. 12(a) and 12(b) are directed to an embodiment of a bonding sheetfor bonding the chip and the die pad. As seen in the drawing, the sheet110 is made of pure silver plate of 20 μm thick, and the grooves 111 of10 μm deep are formed on one side of the sheet. The grooves are formedby press manufacturing or half cut manufacturing with a dicing plate.The Ag sheet is annealed after roll manufacturing and groovemanufacturing so that the hardness of the Ag sheet becomes equal to orless than 35 Hv.

By using the Ag sheet of the present embodiment for performing thethermosonic thermocompression bonding of the chip/die pad, thecomposition deformation of the Ag sheet is facilitated by the presenceof the grooves and softness of the material, and tight and high heatresistant bonding can be achieved without damaging the chip, becausenewly generated planes are formed and the bonding process is performedreadily at the boundary of the bonding planes under the condition thatthe stress added to the Si chip is small. And, a semi-conductor packagehaving high temperature cycle reliability can be provided, because thethermal strain between the chip/die pad accompanied with heat generationof the chip during use of the package can be absorbed by the soft Agsheet having the groove space.

FIG. 13 shows one of the other embodiments of the bonding sheet forbonding the chip and the die pad. In accordance with FIG. 13, the coreportion 112 of the bonding sheet is an Ag sheet manufactured in the sameway as the Ag sheet indicated with reference to FIGS. 12(a) and 12(b).The surface of the Ag sheet is plated with Sn 113 to 0.3-2.0 μm thick.

By using the bonding sheet of the present embodiment for performing thethermosonic thermocompression bonding of chip/die pad, a liquid phase isformed at a temperature above 220° C. by a Ag—Sn reaction, and thesurface of the sheet is covered with a thin film of the liquid.Therefore, an advantage is realized in that ensured and tight bondingcan be achieved readily under a low compression condition, because theliquid in the region where the sheet is compressed to the die pad orchip rear plane electrode is ejected outside and the bonding between themembers having a high melting point is readily performed. Furthermore,because Ag is supplied by dissolving or diffusion during heating fromthe core to the Ag—Sn layer ejected from the bonding interfaces, themelting point of the Ag—Sn layer is elevated finally to higher than 470°C., and the bonding portion can have a high heat resistance. Regardingthe reliability of the semiconductor package, the same advantages as theembodiment indicated in FIG. 1 can be obtained.

FIGS. 14(a) and 14(b) show one of the other embodiments of the bondingsheet for bonding the chip and the die pad. As seen in the drawing, thebonding sheet is a mesh shaped sheet composed of Ag wires 114, 115 wovenin vertical and horizontal directions.

In accordance with the present embodiment, the bonding sheet has bumpsand dips, where the thickness at the portion where the Ag wires areoverlapped is thick and the thickness at the other portion is thin.Therefore, the composition deformation at the thick portion can proceedreadily, and the same advantages as the embodiment indicated withreference to FIGS. 12(a) and 12(b) can be obtained.

FIG. 15 indicates an embodiment of the semiconductor package of thepresent invention, wherein Ag particles are used for bonding the chipand the die pad. In accordance with FIG. 15, the Al electrode 121 isformed on the circuit forming plane of the semiconductor chip 120, andplural Ag bumps 125 are formed thereon. On the rear plane of the chip,the rear plane electrode 122, the outermost surface of which is platedwith Ag, is formed. The lead 123, which is plated with precious metal,on the circuit forming plane and the Ag bumps are directly bonded bythermosonic thermocompression bonding. The chip rear plane electrode 122and the die pad terminal 124, which is plated with precious metal, arebonded by thermosonic thermocompression bonding with the Ag particles126 interposed therebetween, which particles are composed by mixing Agwith the resin 127 in a ratio of more than 90% by volume Ag. The amountof the resin is determined to be so small that the resin pushed outduring the compression does not flow down from the side plane of the diepad terminal onto the compression stage, but in a sufficient amount thatthe mixture can be treated as a viscous liquid. The resin is athermosetting resin, and the resin is cured by heating at the time ofbonding. The Ag particles and the Ag deposition film at the rear planeof the chip, the Ag particles and the die pad terminal, and the Agparticles themselves are bonded partly by metal bonding in the region ofthe contacting portions. The size of the die pad terminal is as large asis capable of being contained into the resin body 128, and is the sameas the size of the chip. It may be somewhat larger or smaller than thechip.

In accordance with the present embodiment, a small and thinsemiconductor package having a low electrical resistance, and containingno Pb can be provided. Because the Ag particles are mixed with resin,dispersion of the Ag particles can be prevented by the viscous propertyof the resin, and the productivity can be improved by the ease of the Agparticle supply to the bonding portion. Because narrow gaps between theAg particles after bonding can be filled with the mixed resin, thenecessity to fill the gaps with the molding resin can be eliminated, anadvantage is realized in that the generation of voids can be decreasedsignificantly and the production yield can be increased. Furthermore,although the bonding agent is a mixture of the resin and Ag particles,the thermocompressing bonding method using concurrently ultrasonicvibration is used for the bonding. Therefore, the resin is pushed outfrom the bonding interface of the metals and a tight bonding of metalseach other is achieved at the bonding portion. Accordingly, an advantageis achieved in that the bonding reliability is remarkably improved incomparison with the adhesion obtained with the use of Ag paste.

FIG. 16 indicates an embodiment of the semiconductor package of thepresent invention, wherein a Ag sheet having grooves is used for bondingthe chip and the die pad. In accordance with FIG. 16, the Au balls 139are formed on the Al electrode 131 of the chip 130, and an Ag depositionfilm is formed on the outermost surface of the rear plane electrode 132.The surfaces of the lead terminal 135 and the die pad terminal 138 areplated with Pd. The Ag sheet 140, whereon the grooves 141 are formed, isinserted between the rear plane of the chip and the die pad terminal.Each of the bonding portions is directly bonded by a thermo-compressionbonding method concurrently using ultrasonic vibration. The leadterminals protrude from a side plane of the resin body and aremanufactured to be folded. The reference numerals 133 and 137 in FIG. 16indicate a Cu core, the reference numerals 134 and 136 indicate a platewith Pd, and the reference number 142 indicates a resin body.

In accordance with the present embodiment, in addition to the advantagesprovided by the embodiment indicated in FIG. 2, breakage of therespective bonding portions of the Al electrode/Au ball/lead terminal bythermal strain and the like can be decreased, and the reliability of thesemiconductor package can be improved, because the resin bonding area atthe upper and lower regions of the lead terminals can be made as wide asthe amount of the lead terminals protrude from only one side, and acompression force between the lead/chip due to the force of the curingshrinkage of the resin can be increased.

FIG. 17 indicates an embodiment of the semiconductor package of thepresent invention, wherein a part of the lead terminal is exposed at theupper plane of the resin body. In accordance with FIG. 17, the Au balls154 are formed on the Al electrode 146 of the chip 145, and an Agdeposition film is formed on the outermost surface of the rear planeelectrode 147. The surfaces of the lead terminal 150 and the die padterminal 153 are plated with Pt/Au 149, 152. The Ag sheet 155, whereonthe grooves 156 are formed, is inserted between the rear plane of thechip and the die pad terminal. Each of the bonding portions is directlybonded by thermo-compression bonding while concurrently using ultrasonicvibration. The lead terminals protrude from a side plane of the resinbody and are manufactured to be folded, and the lead terminal is exposedat the upper surface of the resin body. The reference numerals 148 and151 in FIG. 17 indicate a Cu core, and the reference numeral 157indicates a resin body.

In accordance with the present embodiment, in addition to the advantagesprovided by the embodiment indicated in FIG. 2, the heat resistance ofthe semiconductor package can be decreased significantly, because theheat can be released effectively from the wide area of the lead terminalexposed at the upper surface of the resin body.

FIG. 18 indicates an embodiment of the wiring substrate for mounting thesemiconductor package of the present invention. In accordance with FIG.18, the wiring substrate 160 is a multi-layered organic substratecomposed by laminating substrates, which are composed by forming a Cufoil pattern on an epoxy-glass cloth composite. Various semiconductorpackages and connection terminals 165, 169, 170, 171 of passive devicesare formed on the surface of the substrate. The connection terminals formounting the semiconductor of the present invention are composed of theconnection terminals 161, 168 for the drain, the connection terminals164, 167 for the source, and the connection terminals 162, 163, 166 forthe gate, all of which are in a size that is containable in the body ofthe package. FIG. 19 indicates an embodiment of an electronic device,wherein the wiring substrate indicated in FIG. 18 is mounted with thesemiconductor packages of the present invention, LST packages, andelements. In accordance With FIG. 19, the LSI packages 176, 177, 178 forsignal processing, the vertical semiconductor packages 172, 175, and theresistance and passive device of capacitance 173, 174 are mounted on thewiring substrate by soldering connection. The reference numeral 184 b inFIG. 209 indicates an external connection terminal for drain.

In accordance with the present embodiment, the connecting area betweenthe power semiconductor package and the substrate can be wide, and thechip, i.e. a heater, and the substrate can be connected with theshortest distance. Therefore, the temperature difference between thesubstrate and the package can be decreased, the stress generated at thesolder connecting portions can be decreased, and a highly reliableelectronic device can be provided. Because heat generation of thepackage is decreased, the temperature of the device is not elevatedbeyond the normal operating temperature range, even though no specialheat releasing device is provided. Accordingly, such advantages arerealized that the structure of the electronic device can be simplified,cost is suppressed, and the life of the electronic device can beimproved due to the low temperature rise during operation.

As explained in detail above, in accordance with the present invention,the electrical resistance of the package can be decreased.

FIG. 29 indicates changes of strength at the bonding portions, when Auball bonding is performed on the Al electrode film of 3.5 μm thick at200° C. of bonding temperature, and the bonding portions are held at ahigh temperature. When the holding temperature is lower than 200° C., adecrease of the strength can be observed in a short time, but the higherthe holding temperature is, the sooner the strength is increased again.As the holding time is further extended, the strength is decreasedagain. As the result of analyzing the reason for the above phenomenon indetail, it was revealed that the strength immediately after the bondingdepends on the strength of the Al film itself; and, the first decreaseof the strength at the initial stage of holding at the high temperatureis caused by growth of an AuAl₂ compound, which is known conventionallyand called a purple plague, at the boundary of a AuAl alloy layer andthe Al film. Furthermore, it was revealed that the increase in strengthis caused by changing all the Al film at the bonding portion to the AuAlalloy layer, which is stronger than Al, and the subsequent decrease inthe strength is caused by growing defects known as carkendahl voids atthe boundary plane of the Au/AuAl alloy layer. It was found that theincrease in the strength as much as twice the bonding strength is causedby the presence of fine bumps and dips on the surface of the transistorchip corresponding to structure having a large number of cells, and thealloy layer and the Si substrate forms a mechanical meshing structure.This is a phenomenon which does not occur with conventional LSI devices.It was found that, after performing a heat treatment for a short time ata high temperature higher than 250° C., growth of the carkendahl voidsdid not become any problem at a heating temperature of 150° C. and aholding time of 2000 hours, and the decrease in the strength was notgenerated, as indicated in FIG. 30. The inventor of the presentinvention utilizes the above phenomenon and has achieved an improvementof the initial bonding strength by as much as approximately twice, andthe improvement of the reliability for connection at the metallicbonding portions themselves during the temperature cycle in the regionlower than 150° C., i.e. the temperature for practical use, and holdingat a high temperature. Furthermore, with regard to the bonding the leadfor an electrode with the Au bumps on the chip, an thermosonicthermocompression bonding method, which is performed under a lowtemperature (lower than 250° C.) and a low load without damaging thechip, has been developed, which makes it possible to bond at a lowtemperature. Accordingly, in view from the above, thermal straingenerated during the cooling step in the bonding operation could bedecreased significantly, and the reliability of the connection at themetal bonding portions could be improved. Simultaneously, in accordancewith realization of the low temperature bonding method, it becomespossible to perform metallic bonding and resin adhesion simultaneouslyby filling the resin into the gap between the electrode lead/chip whenbonding the electrode lead/chip. Then, because the resin is pushed outby compression, resin can be filled with no void, and because thebonding can be achieved in a condition wherein a compression force isadded to the Au bumps by a curing shrinking phenomenon of the resin, thefatigue life can be extended by the effect of the compression stress,even if a temperature cycle is added.

Next, a high reliability package, which does not contain Pb and has noresin sealing, will be explained hereinafter. The transistor package iscomposed of a structure, wherein three independent metallic componentsare connected electrically with respective electrodes of the chip andfixed in the structure. Conventionally, the fixing of the respectivemetallic components has been performed with use of a cured resin.However, in accordance with the structure of the present invention, themetallic components are fixed by bonding the respective component withthe chip flexibly and tightly by concurrent use of metallic bonding andresin adhering. The reason to use the metallic bonding and the resinadhering concurrently is that, although a high strength can be achievedby use of only the metallic bonding, if the cu, which is a core materialof the metallic component, is bonded with the Si chip tightly, a largestrain is generated in the Si chip due to the difference of thermalexpansion of the Cu and the Si chip, and deterioration of theircharacteristics, or in an extreme case, damage of the chip can begenerated. Therefore, it is necessary to make the bonding portion have aflexible structure for absorbing the strain, and as the metallic bondingstructure having spaces, the structure of the present invention, whereininsufficient bonding strength is reinforced by resin adhesion, isrealized. In accordance with the structure of the present invention, ifthe resin is used in the form of a film, the resin adhering and themetallic bonding can be performed in the same bonding step,simultaneously, the mold-bake step of the resin can be omitted.Accordingly, the production cost can be decreased, the productivity canbe improved, and the transistor package, which is desirable in view ofenvironmental problems, can be provided. In accordance with performingthe metallic bonding by a thermosonic thermocompression method, bytreating the surface of the metal with spatter cleaning before bonding,and by changing the bonding force from low loading to high loading in aslope shape under adding the ultrasonic waves; metallic bonding having ahigh strength under the condition that the deformation of the bumps issmall can be achieved.

Hereinafter, embodiments of the present invention will be explained indetail with reference to the drawings.

FIGS. 22(a) and 22(b) are directed to an embodiment of the transistorpackage relating to the present invention. In accordance with FIG.22(a), the Al electrode 402 of 2 μm thick is formed on the circuitforming plane of the transistor chip 401, and the rear plane electrode403, the outermost surface of which is plated with Au, is formed on theopposite plane of the transistor chip 401. The Au bumps 407 are formedon the Al electrode by a ball bonding method. In this step, all the Alelectrode film under the bumps is changed to a AuAl alloy 409 by heattreatment of, for instance, 300° C.—2 hours, or 250° C.—10 hours. Thesurface of the metallic lead 404, 405 is plated with Pd/Au, and themetallic leads are bonded with the Au bumps formed on the Al electrodeby an incorporated thermosonic thermocompression bonding method at arelatively low temperature, such as lower than 250° C. The first resin408 is supplied in the form of sheet at the thermosonicthermocompression bonding, and is adhered and cured simultaneously withthe bonding of the Au bumps. The height of the bumps (resin thickness)after bonding is several tens microns. The chip rear plane electrode andthe die pad mounting lead 406 hold between them the second resin 411sheet, wherein precious metal particles are buried, and the chip rearplane electrode and the die pad mounting lead 406 are bonded bycompression with the addition of ultrasonic waves and heating at arelatively low temperature such as lower than 250° C. The precious metalparticles, i.e. Ag particles 410 in this case, are deformed bycompression from the rear electrode and the die pad, and a metallicbonded condition results. The die pad mounting leads are manufacturedpreviously to be folded, and the bonding condition is controlled so thatthe lower plane after deforming and bonding of the Ag particles isapproximately in a same plane as the plane of the electrode lead. Thefirst and second resin adhere to the upper and the lower members, andgive a compression stress to the bonding portion due to the shrinkingphenomenon at the curing time. Here, a thermo-adhering polyimide resinis used as the first and second resin, but an epoxy resin, which can becured at room temperature, or another resin may be used.

In accordance with the present embodiment, the strength at the bondingportions of the Al electrode/Au bump/electrode lead can be increased bymaking all of the Al under the bonding portions of the transistorpackage an alloy, while a decrease of the strength by holding thebonding portions at a high temperature is prevented, and a structure,wherein the compression force is applied to the bonding portions by theeffect of the resin adhering, is composed. Accordingly, a highlyreliable and low resistant transistor package having a significantlyextended temperature cycle life can be provided. Because the bondingtemperature in the compression bonding of the metals to each other islowered to lower than 250° C., concurrent bonding with the resinadhering becomes possible, and filling and adhering the resin with novoids also becomes possible. Furthermore, the residual stress at thebonding portions can be decreased by lower temperature bonding.Accordingly, in view of the above points, the reliability of thetransistor can be improved.

In accordance with the bonding structure, wherein the rear planeelectrode of the chip and the die pad mounting leads are bonded byconcurrent use of the metallic bonding and the resin adhering, of thepresent embodiment, and thermal and electrical conductivity at thebonding portions are ensured, and simultaneously, the difference inthermal expansion between the chip and the die pad mounting leads areabsorbed by the deformation of the space filled with the resin.Furthermore, the temperature cycle life of the die pad-bonding portionscan be improved by a compression load applying effect on the metallicbonding portion accompanied with the curing shrinkage of the resin, andthe package containing no Pb, having concurrently desirable electricaland thermal conductivity, temperature cycle reliability, and solderreflow endurance can be provided.

Furthermore, for the above two reasons, the reliability of the packagecan be ensured without performing a resin sealing. Accordingly, a smallsize and low resistant transistor package, which can save resin,decrease the production cost and the production time by omitting themolding step, and is desirable in view of environmental problems, can beprovided.

Because the bonding portions of the Al electrode and the Au bumps arechanged to a Au—Al alloy for strengthening by heat treatment in the stepto bond the chip with the electrode lead via Au bumps by the thermosonicthermocompression bonding method, even if the Au bumps are ruptured byadding a load and vibration from the chip side or the lead side forcompression bonding, the Si substrate or the transistor element underthe bumps is not damaged, such as by generation of cracks. Accordingly,generation of failed products by the bonding damage can be prevented,and the production yield can be improved.

FIG. 23 indicates one of the other embodiments of the transistor packagerelating to the present invention. In accordance with FIG. 23, an Alelectrode 416 of 5 μm thick is formed on the circuit forming plane ofthe transistor chip 415, and the rear plane electrode 417, the outermostsurface of which is made of Ag, is formed on the opposite plane. Thereference numeral 418 in FIG. 23 indicates a lead. The Au bumps 420 areformed on the Al electrode by a ball bonding method. The referencenumeral 423 in FIG. 23 indicates a Ag bump. In this step, all of the Alelectrode film under the bumps is changed to a Au—Al alloy layer 421 byheat treatment of, for instance, 300° C.—2 hours, or 250° C.—10 hours.The openings 425, 426 are formed in the chip facing regions of theelectrode lead 416 and the die pad mounting lead 419, and all of thesurface of the members is plated with Pd/Au flush plating. The electrodelead is bonded with the Au bumps formed on the Al electrode by anincorporated thermosonic thermocompression bonding method at arelatively low temperature lower than 200° C. The first resin 422 issupplied in the form of sheet, and adhered and cured simultaneously withthe bonding of the Au bumps. The height of the Au bumps (resin height)is several tens microns. The chip rear plane electrode and the die padmounting leads hold between them the second resin 424 in the form of asheet, wherein precious metal particles are buried and the chip rearplane electrode and the die pad mounting lead are bonded by compressionwith the addition of ultrasonic waves and heating at a relatively lowtemperature lower than 250° C. The precious metal particles, i.e. theparticles made of Ag in this case, are deformed by compression from therear electrode and the die pad mounting lead with heating, compressing,and ultrasonic vibrating, and a metallic bonded condition results. Thefirst and second resin are adhered to the upper and the lower members,and give a compression stress to the bonding portion due to theshrinking phenomenon at the curing time.

In accordance with the present embodiment, a package of high reliabilityand low resistance, and which is desirable in view of environmentproblems can be provided as well as the package indicated in FIG. 22(a).Furthermore, because the electrode and the resin, and the die padmounting lead and the resin are bonded tightly by mechanical bonding atthe openings, in addition to the chemical bonding (adhering) at theboundary plane, peeling off of the resin adhered portions does not occureven under a high temperature and high humidity environment and thetemperature cycle environment, the strain added to the metallic bondingportions of the Au bumps and Ag particle can be decreased, and thereliability of the package can be improved significantly.

FIG. 24 indicates one of the other embodiments of the transistor packagerelating to the present invention. In accordance with FIG. 24, the Alelectrodes 431, 432 of 3.5 μm thick are formed on the circuit formingplane of the transistor chip 430, and the rear plane electrode 433, theoutermost surface of which is Ag, is formed on the opposite plane. Thereference numerals 434, 437 and 438 in FIG. 24 indicates a Cu core. TheAu bumps 433 are formed on the Al electrode by a ball bonding method.All of the surface of the members of the electrode leads 436, 439 andthe die pad mounting lead 442 are plated by Pd/Au flush plating 435,438, 441. The electrode leads and the Au bumps formed on the Alelectrode are bonded by the incorporated thermosonic thermocompressionbonding method at a relatively low temperature lower than 200° C. Thefirst resin 441 is supplied in a liquid state to fill into gaps afterthe thermosonic thermocompression bonding, and is adhered and cured. Thechip rear plane electrode and the die pad mounting leads hold betweenthem the second resin 448 in the form of a sheet, wherein precious metalparticles are buried, and the chip rear plane electrode and the die padmounting lead 442 are bonded by compression with the addition ofultrasonic waves and heating at a relatively low temperature lower than250° C. The precious metal particles 447, i.e. the particles made of Cu445 of 30 μm, the surface of which is plated with Ag 446 to 5 μm thickin this case, are deformed by compression from the rear electrode andthe die pad mounting lead with heating, pressing, and ultrasonicvibration, and a metallic bonded condition. The first and second resinare adhered to the upper and the lower members, and give a compressionstress to the bonding portion due to the shrinking phenomenon at thecuring time. The two electrode leads and the die pad mounting lead arearranged at opposite planes respectively with the chip interposedbetween them, and the size of each lead is approximately the same as thesize of the chip.

In accordance with the present embodiment, a package of high reliabilityand low resistance, and which is desirable in view of environmentproblems can be provided as well as the package indicated in FIG. 22.Furthermore, because Ag plated Cu particles having cores made of Cu,which is cheaper than a precious metal, are used for bonding the chiprear plane electrode with the die pad mounting lead, the component costcan be decreased. Further, because the planes of the external connectionterminals are arranged at upper and lower sides of the chip, astructure, wherein the mounting can be performed by holding the packagefrom both sides of the chip, can be adopted, and the mounting bymechanical contact can be performed readily. A chip size package can berealized, and high density mounting becomes possible by decreasing themounting area.

FIG. 25 indicates one of the other embodiments of the structure of thetransistor package relating to the present invention. In accordance withFIG. 25, an Al electrode 451 of 3.5 μm thick is formed on the circuitforming plane of the transistor chip 450, and the rear plane electrode452, the outermost surface of which is plated with Au, is formed on thesurface of the opposite plane. The reference numerals 453 and 456 inFIG. 25 indicate a Cu core, and the reference numeral 457 indicates aplate with a precious metal. The Au bumps 461 are formed on the Alelectrode by a ball bonding method. The reference numeral 463 in FIG. 25indicates a resin body. In this step, all the Al electrode film underthe bumps is changed to a Au—Al alloy layer 462 by heat treatment of,for instance, 300° C.—2 hours, or 250° C.—10 hours. The surface of theelectrode lead 455 is plated with Pd/Au 454, and the electrode leads arebonded with the Au bumps formed on the Al electrode by an incorporatedthermosonic thermocompression bonding method at a relatively lowtemperature lower than 200° C. The chip rear plane electrode and the diepad leads hold between them the die pad bonding resin 460 in the form ofa sheet, wherein precious metal particles 459 are buried, and the chiprear plane electrode and the die pad lead 458 are bonded by compressionwith the addition of ultrasonic waves and heating at a relatively lowtemperature lower than 250° C. The precious metal particles 447, i.e.the particles made of Ag in this case, are deformed by compression tothe rear electrode and the die pad mounting lead with heating, pressing,and ultrasonic vibrating, and a metallic bonded condition results. Allof the chip and the respective leads are covered with mold resin exceptthe external connection terminals. A compression stress is applied tothe bonding portions of the chip and each of the leads by the shrinkingphenomenon of the resin at the curing time.

In accordance with the present embodiment, the bonding portion of the Aubumps with the Al electrode film I-S strengthened to twice the normalstrength by alloying to the Au—Al alloy, and the AuAl₂ compound having aweak strength, which is generally formed by holding the package at ahigh temperature, is not formed. Therefore, a low resistance transistorpackage having superior temperature cycle reliability can be realized.

FIG. 26 indicates an embodiment of the die pad-bonding adhering film ofthe present invention.

In accordance with FIG. 26, the precious metal particles 466 are buriedinto the resin film 465 under a condition wherein a part of the particleis exposed at the surface of the resin film. The precious metal particleis selected from the group consisting of Ag, Au, Pd, Pt, and particlesobtained by plating Cu, Ni cores with Ag, Au, Pd, and Pt, respectively.The sizes of the particles are composed such that a large number of theparticles having at least a half of the film thickness are containedtherein. The resin film is selected from the group consisting ofpolyimide resin, epoxy resin, polyester resin, and phenol resin, and theresin is manufactured to a condition wherein thermoplastic andthermosetting properties are concurrently provided (a condition that thesolvent is evaporated and the resin is semi-cured).

FIG. 27 indicates one of the other embodiments of the die pad-bondingadhering film of the present invention.

In accordance with FIG. 27, the precious metal particles 468, 469 areexposed to both surfaces at the resin film 467.

FIGS. 28(a) to 28(c) are directed to indicates a method for adhering twomembers using the die pad-bonding film indicated in FIG. 26. In the stepshown in FIG. 28(a), the chip member 470, whereon a precious metal thinfilm is deposited, the die pad-bonding film 471, wherein Ag particles472 are buried, and the die pad mounting lead 473, the bonding plane ofwhich is plated with thick Ag, are laminated and positioned. Then, inthe step shown in FIG. 28(b), the laminated work is placed on theheating stage 474 and is compressed by applying the load 478 with thebonding tool 476 via the organic film 477. The reference numeral 475 inFIG. 28(b) indicates a heater. At the time when the temperature of thework is elevated to a designated temperature, ultrasonic vibration 479is applied to the bonding tool in order to push in the chip member intothe die pad-bonding film while rupturing the Ag particles for metallicbonding of the chip member with the die pad mounting lead via the Agparticles, thereby adhering the chip member and the die pad mountinglead via the die pad-bonding film. The temperature at the start ofapplication of the ultrasonic waves is the temperature at whichsoftening of the die pad-bonding film begins, and the final heatingtemperature is the temperature at which the die pad-bonding film iscured. The organic film interposed between the bonding tool and the chipmember is changed at every operation or per several operations.Accordingly, a method is adopted in which the organic film is suppliedin a rolled tape state and is transferred in an orderly manner to theoperating portion. The material of the organic film is composed of anorganic material having a high glass transition temperature, which doesnot become soft at the bonding temperature. The condition after bondingis indicated in FIG. 28(c). The chip member and the die pad mountinglead are bonded metallically at plural portions via one or two of the Agparticles, and an excess amount of the die pad-bonding film is pushedoutside from the gap between the both members. Accordingly, no void isgenerated in the resin filling the gap.

In accordance with the present embodiment, a clean metallic surface ofthe Ag particle can be compressed onto the chip member, because the Agparticles are exposed out from the is die pad-bonding film; the Agparticle can be deformed certainly, and microscopic plastic flow of bothmetallic members is generated, because the size of the Ag particle ismade larger than the gap; and the ensured metallic bonding becomespossible by adding the ultrasonic vibration. On the other hand, inaccordance with the bonding step of the Ag particles with the die padmounting lead, the Ag particle contacts the die pad mounting lead bypushing away the resin film, which is softened by elevation of thetemperature, in the step in which laminated work is placed on theheating stage and the load is applied by the bonding tool via the chip.At this time, the resin is still in a solid state and does not make thesurface of the metal wet, and the Ag particle and the die pad mountinglead can contact each other with a clean metallic boundary. Therefore,ensured metallic bonding becomes possible by adding the ultrasonicvibration. The resin first reaches a liquid state by heating after tightcontact of the Ag particles and the die pad mounting lead. After theexcess amount of the resin is pushed outside through the gap between thechip and the die pad mounting lead, its curing starts. In accordancewith the phenomenon described above, the two members are certainlybonded metallically via the Ag particles, and, simultaneously, theadhering with the resin proceeds concurrently. Therefore, the number ofthe bonding steps can be decreased, and improvement of the productivitycan be realized.

The reference numeral 481 in FIG. 29 indicates a Si substrate, thereference numeral 482 indicates an Al film, the reference numeral 483indicates a Au bump, and the reference numeral 484 indicates a AuAlalloy. The reference numeral 485 in FIG. 30 indicates a Si substrate,the reference numeral 488 indicates a AuAl alloy, and the referencenumeral 489 indicates an electrode lead.

Because the organic film is inserted between the bonding tool and thechip member as a consumable article, damage to the chip member bycontact with the hard bonding tool can be prevented, and the productionyield of the package can be increased. Furthermore, consumption of thebonding tool can be prevented, and the usable cycles of the apparatuscan be increased significantly. Accordingly, a decrease of theproduction cost can be realized.

As described above in detail, in accordance with the present invention,the semiconductor package, wherein the strength of the bonding portionsof Al the electrode/Au bumps/electrode lead is increased, can beprovided.

FIG. 31 indicates an embodiment of the present invention in a case whenthe bump containing precious metal at the front plane side electrode ismade of an alloy with low melting point metals.

In accordance with FIG. 31, the metallized film 289 of Ti/Ni/Au,Ti/Ni/Ag, Cr/Cu/Ni/Au, or Cr/Cu/Ni/Ag, in a specified pattern is formedon the front plane side Al electrode pad 282 of the verticalsemiconductor element 281, and the metallized electrode 283, theoutermost surface of which is Ag or Au, is formed on the rear sideplane. The die pad 286 is connected metallically all over the surface ofthe metallized electrode 283 by the solder 287 containing Ag—Sn as abasic composition, for instance, Ag—Sn—Pb, Ag—Sn—Pb—Cu, and the like.The lead 284 is connected metallically with the front plane sidemetallized film 289 by the alloy bumps 285 containing Ag—Sn as a basiccomposition. The connecting portion is formed only in a specifiedregion, wherein the metallized film 289 of the front plane sideelectrode is formed. The semiconductor element, the lead, and a part ofthe die pad is protected by covering them with resin 288. The lowerplane of the die pad is exposed to the surface of the resin body and isreshaped in a condition that the die pad protrudes out horizontally fromthe plane of the resin body opposite to the lead. The lead protrudesfrom the middle portion of the side plane of the resin body and isfolded so that the lower plane of the lead is reshaped to beapproximately at the same level as the lower plane of the die pad. Here,approximately the same includes a range in which the difference inheight is within the thickness of the lead or the die pad.

FIG. 32 indicates an embodiment of the present invention for a case inwhich the semiconductor package indicated in FIG. 31 is mounted on awiring substrate.

In accordance with FIG. 32, a Ni/Au film is formed on the surface of theconnecting terminals291, 293 formed on the wiring substrate 290, and thelead 284 of the package is connected to the lower plane of the die pad286 with a low melting point metal, which is able to form a connectionat an operating temperature lower than the melting point of theconnecting alloy 285, 287 in the package. The reference numeral 296 inFIG. 32 indicates a die pad. When the connecting alloy in the package isselected from the Ag—Sn—Cu group, the wiring substrate connecting alloyis a solder of the Sn—Bi group or Sn—In group. When the connecting alloyin the package is selected from the Ag—Sn—Pb group, a solder of theSn—Ag group is used as the wiring substrate connecting alloy.

In accordance with the present embodiment, the chip electrode and thelead are connected by the bumps. Accordingly, because the connectiondistance is short and the connecting area, that is, the conducting area,is wide, the electrical resistance at the connecting portion can bedecreased. By forming the bumps with an alloy composed of a preciousmetal added with low melting point metals, the amount of the preciousmetal being used can be decreased, and the surface of the leads can becomposed with the low melting point metals. Accordingly, the cost forthe members can be decreased. On the contrary, when the surfaceelectrode is connected with a fused alloy, a short circuit between theadjacent two electrodes becomes a problem. However, in accordance withthe present embodiment, the metalized film, which is wettable with theconnecting alloy formed on the chip side electrode, is restricted toform in a specified region. Accordingly, even if the distance betweenthe electrodes is short, a short circuit can be prevented, because thefused metal is not spread widely, nor comes too close. In accordancewith the present embodiment, the chip electrode is connected to theupper and lower metallic members with the fused metal, and no externalforce is added to the chip electrode during the connection operation.Therefore, the assembling yield can be increased by preventing damage tothe chip, and the cost for production can be decreased. Because the padprotrudes from the side plane of the resin body horizontally, thesoldering portion for mounting onto the wiring substrate is visible, sothat soldering failure can be inspected readily and generation of adefective product can be prevented.

In accordance with the present embodiment, the low melting point alloycontaining a precious metal is used as the material for the bumps, but alow melting point alloy containing no precious metal has the sameadvantages as the present embodiment.

FIG. 33 indicates an embodiment of the present invention for a case inwhich, the semiconductor package of the present invention, die pad ofwhich is omitted, is mounted on the wiring substrate.

The reference mark 255 indicates a Cu core, the reference numeral 259 bindicates a connection pad (a and b are same), and the referencenumerals 260 a and 260 b indicate a solder.

In accordance with FIG. 33, the Au bumps 257 are formed on the frontplane side Al electrode pad 252 of the vertical type semiconductor chip251, the bumps are connected metallically to the lead 256 plated withprecious metal, and the periphery of the bumps is reinforced by theresin 261. The metalized electrode 253 at the rear plane of the chip isconnected directly to the connection pad 259 of the wiring substrate 258with the solder 260. The external connecting plane of the lead isconnected to the connecting terminals with the same kind of solder. Themetalized electrode plane at the rear plane of the chip and the externalconnecting plane of the lead are formed so that their height becomeapproximately to the same level, in other words, the difference of theheight is within the thickness of the lead. In accordance with FIG. 33,the lead and the chip are exposed outside in the condition mounted ontothe substrate. However, if the environment is not desirable, the leadand the chip may be covered with a second resin by potting.

In accordance with the present embodiment, the die pad is not used, andthe package structure becomes simple. Therefore, the cost for assemblingand the cost for the components can be decreased, and the productioncost can be decreased significantly. Because the electrode at the rearplane of the chip is connected directly to the connecting terminals ofthe wiring substrate by soldering, the electrical resistance betweenthem can be decreased, and the on-resistance of the package can bedecreased. The height of the package can be decreased to the extent thatthe die pad omitted, and so an ultra thin substrate mounting can berealized. If the package is sealed with a potting resin after mounting,the temperature cycle reliability at the connecting portion at the rearplane of the chip is improved in comparison with the conventionalstructure using the die pad, and an electronic apparatus having a highreliability can be realized.

FIG. 34 indicates an embodiment of the present invention for a case inwhich the plane mounting type semiconductor package of the presentinvention is mounted on a wiring substrate.

The reference numeral 263 in FIG. 34 indicates an Al electrode pad, thereference numeral 264 indicates a metalized electrode, the referencemark 265 indicates a Cu core, the reference numerals 266 and 270indicate a plate with precious metal, the reference numeral 273indicates a wiring substrate, and the reference numeral 274 indicates aconnection pad.

In accordance with FIG. 34, the Au bumps 268 are formed on the Alelectrode pad of the vertical type semiconductor chip 262, the bumps areconnected metallically to the lead 267, the surface of which is platedwith a precious metal. A metalized layer, the outermost surface of whichis a precious metal, is formed at the rear plane of the chip, and themetalized layer is connected electrically to the die pad 269 plated witha precious metal with precious metal particles 271. The chip, the lead,and a part of the die pad are covered with the resin 272 for protectionand reinforcement. The lower plane of the die pad is exposed to thebottom surface of the resin body and protrudes to the side plane. On theother hand, the lead protrudes from the middle portion of the oppositeside plane of the resin body and is manufactured to be folded so thatthe height of the external connecting portion becomes approximately thesame as the height of the external connecting portion of the die pad.The plane mounting is performed by connecting to the connectingterminals of the wiring substrate by soldering. Because the connectingterminals are aligned approximately at a definite height in the range ofseveral tens of microns, the external connecting terminals of thepackage must be aligned with their height. In accordance with thepresent embodiment, a small variation in height can be absorbed by thedifference of the thickness of the solder 275, and the allowabledifference of the height (ΔH) is the same as the difference in thethickness of the lead (smaller than approximately several hundredsmicron). The plane mounting package may be any package, if thedifference of the external connecting plane facing the wiring substrateof which is controlled to within the thickness of the lead or the diepad.

In accordance with the present embodiment, a structure, wherein the diepad protrudes from the side plane of the resin body, is adopted.Accordingly, the solder connecting portion can be confirmed visuallyfrom the top side when the package is mounted onto the wiring substrate,whereby the connecting portions can be inspected readily, and productionvelocity is increased. Furthermore, the cost for assembling can bedecreased, and the operability is improved.

FIG. 35(a) indicates a plan view of the vertical semiconductor elementused in assembling the semiconductor package by the present invention,and FIG. 35(b) shows an example of its cross sectional structure. Thereference numeral 311 in FIG. 35(a) indicates a transistor chip, thereference numeral 312 indicates a source electrode, and the referencemark 313 indicates a gate electrode pad.

In accordance with FIG. 35(b), n-type epitaxial layer 315 is formed onthe high concentration n-type substrate 314, and p-type and n-typepatterns are formed in the layer in a condition wherein the depths andshapes are controlled. The gate oxide film 316 is formed at a position,which includes the p-type diffusion layer 316 formed so as to surroundthe contact area of the source electrode, and n-type layers 317, 318, atright and left. The gate electrode line 320 is formed on the oxide film.The gate electrode line is coated with the insulating layer 321 so asnot to contact the source electrode pad 312 and is connected to the gateelectrode pad 313. The reference numeral 319 in FIG. 35(b) indicates ametal oxide, the reference numerals 320 a and 320 b indicate a gateelectrode line, the reference numerals 321 a, 321 b and 321 c indicatean insulating layer, and the reference number 322 indicates a metalizeddrain electrode. Generally, aluminum is used as the material of the gateand source electrode pad, but in some cases, another metal is metalizedthereon. Generally, the plane whereon the pattern of the diffusion layeris formed is called the front plane, and the opposite plane is calledthe rear plane. The present element is a so-called MOSFET, whichcontrols the current passing through the source/drain in accordance withthe presence of, or magnitude of, the voltage applied to the gateelectrode. A decrease of the on-resistance of the present element isremarkably advantageous in view of the reduced power loss. An effect todecrease the resistance is achieved by controlling the profile of thenpn structure in the epitaxial layer and the impurity concentration, butthe most effective method is to shorten the conducting distance bydecreasing the thickness of the wafer. Therefore, pn elements, circuitpatterns, and electrode pads are formed on the surface of the Si wafer,the thickness of which makes it possible to handle the wafer in themanufacturing steps. Subsequently, the rear plane of the wafer is groundto make the high density n-type substrate 314 thin, and finally, thedrain electrode metalized layer at the rear plane is formed to producethe element.

In a case when the rear plane ground element of the present embodimentis used, the contacting area with the metalized layer is increased,because the grinding mark at the rear plane forms adequate bumps anddips, and the bumps and dips perform further a role of an anchor effect.Therefore, because the ohmic contact resistance of the rear planeelectrode is decreased, and adherence of the rear plane electrode withthe metalized layer is increased, improved effects in both electricalcharacteristics and reliability can be realized.

The present invention is applicable to not only a MOSFET, but to anyelement, the resistance or impedance of which must be decreased, such asdiodes, thyristors, photo-elements, and the like.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor chip; a first metallic member connected to a main currentelectrode on a circuit forming front plane of the chip; and a secondmetallic member connected to a chip rear plane electrode; a thirdmetallic member connected to a control electrode on the front plane ofthe chip; wherein: said main current electrode and said controlelectrode are composed of any of an Al film and an Al alloy film; pluralAu bumps are formed on the Al electrode film in a metallically bondedcondition; each of said first and second metallic members, which areplated with a precious metal, has such a structure that each is bondedwith said Au bumps by compression bonding, and gaps between the metallicmembers and said chip are filled with resin; and a plane of said secondmetallic member opposite to said chip in a plan view projected directionof the chip, and planes of said first and third metallic membersopposite to said chip are exposed to the surface of said semiconductordevice.
 2. A semiconductor device comprising: a semiconductor chip; afirst metallic member connected to a main current electrode on a circuitforming front plane of the chip; and a second metallic member connectedto a chip rear plane electrode; a third metallic member connected to acontrol electrode on the front plane of the chip; wherein: said maincurrent electrode and said control electrode are composed of any of anAl film and an Al alloy film; plural Au bumps are formed on the Alelectrode film in a metallically bonded condition; each of said firstand second metallic members, which are plated with a precious metal, hassuch a structure that each is bonded with said Au bumps by compressionbonding, and gaps between the metallic members and said chip are filledwith resin; and a plane of said second metallic member opposite to saidchip in a plan view projected direction of the chip is exposed to thesurface of said semiconductor device.